WKS
Protons, Neutrons & Electrons
Name Answer Key
Period
Date
1. Which subatomic particle identifies an atom as that of a particular element? Where in the atom is it located?
How is this particle related to the atom’s atomic number?
The proton, in the nucleus. The number of protons equals the atomic number.
2. Which subatomic particle must be present in equal amount as the particle in question #1 in a neutral atom?
Why is this necessary? (Discuss BOTH particles.) Where in the atom is it located?
The electron. There must be an equal number of electrons and protons. Since the protons have a +1 charge
and the electrons have a –1 charge, the equal numbers of positive and negative charges exactly cancel. It is
outside the nucleus.
3. Which subatomic particle has no electrical charge but contributes to the mass number of an isotope? Where
in the atom is this particle located?
The neutron. It is in the nucleus.
4. What two particles make up almost all of the mass of the atom? Which particle determines the volume?
The proton and neutron together make up the mass of the atom; the electron cloud determines the volume.
5. How is the mass number of an isotope determined?
Mass # = # protons + # neutrons = atomic # + # neutrons
6. Complete the table below. All atoms are electrically neutral.
Atomic
Isotope Name
Symbol
# Protons
Number
a) Carbon-12
12
6
#
Neutrons
Mass
Number
#
Electrons
C
6
6
6
12
6
Ca
20
20
20
40
20
He
2
2
2
4
2
b) Calcium-40
40
20
c) Helium-4
4
2
190
76
Os
76
76
114
190
76
e) Aluminum-27
27
13
Al
13
13
14
27
13
f) Neon-22
22
10
Ne
10
10
12
22
10
C
6
6
8
14
6
d) Osmium-190
g) Carbon-14
14
6
h) Chlorine-37
37
17
Cl
17
17
20
37
17
i) Rubidium-85
85
37
Rb
37
37
48
85
37
j) Californium-252
252
98
Cf
98
98
154
252
98
k) Zinc-65
65
30
Zn
30
30
35
65
30
204
80
Hg
80
80
124
204
80
l) Mercury-204